Ignore hover events while pointers are already down

If pointers are already down from another device, finish the current
gesture and ignore events from other devices.

When multi-device support is enabled, we can remove this restriction.

Bug: 268538505
Test: m inputflinger_tests && $ANDROID_HOST_OUT/nativetest64/inputflinger_tests/inputflinger_tests
Change-Id: I6419b6d118760d285457bc9e5127e055f21ecf7f
diff --git a/services/inputflinger/dispatcher/CancelationOptions.h b/services/inputflinger/dispatcher/CancelationOptions.h
index 48f9f2b..83e6a60 100644
--- a/services/inputflinger/dispatcher/CancelationOptions.h
+++ b/services/inputflinger/dispatcher/CancelationOptions.h
@@ -30,6 +30,7 @@
         CANCEL_POINTER_EVENTS = 1,
         CANCEL_NON_POINTER_EVENTS = 2,
         CANCEL_FALLBACK_EVENTS = 3,
+        ftl_last = CANCEL_FALLBACK_EVENTS,
     };
 
     // The criterion to use to determine which events should be canceled.